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TB10 HB-EZW down near Lucerne

To me it still sounds like crossing a ridge line too low; faced with wind rising over the peak, pushing him down, he pulled back to try and counter the downward force only to have the aircraft stall / spin – the aircraft apparently impacted vertically, with high energy.

Although the plane was destroyed by fire, the investigators have been able to recover an SD card from another Flarm equipped aircraft flying in the vicinity which will allow them to reconstruct the altitude, rate of climb, ground speed and flight direction of the stricken aircraft. The initial investigation will also focus on a radio call made by the pilot as he reached the ridge, by identifying and isolating the aircraft engine noises, they hope to be able to rule out engine issues as part of the cause of the accident.

EDL*, Germany

The SUST has published the final rapport local copy

The reason for the accident which is CFIT are according to the rapport improper flight tactics and the lack of current training on the aircraft type.

The density altitude at the site of the accident was 4700 ft AMSL. According to the analysis of the SUST this means a reduced climb performance of 8%. With full climb performance and VY, according to SUST, an overflight in about 300m AGL would have been possible.

The pilot flew about 5 hours on SEP aircraft during the last 12 month but logged no hours the 90 days prior to the accident on the TB10

After take off the plane flew in direction Lopper, but after reaching the Alpnachersee it flew towards the Renggpass. There it collided with treetops in 2953 ft AMSL and then crashed into the forest where it caught fire and burned out. The pilot had actually wanted to fly out via the Lopper, for which the Pilatus Flight Group specifies a minimum altitude of 3500 ft AMSL. During the climb the rate of climb was low, between 200 and 300 fpm. The SUST assumes that the pilot used a reduced RPM rather than full throttle. The SUST has also analyzed that in climb position the forward visibility was severely reduced and the pilot had little chance to see the ridge in front of him in the last 30 seconds.

The conclusions draw an unfortunately not unusual picture. A very experienced pilot flies with a for him unfamiliar aircraft close to the MTOW according to recommendations that affects flight performance. He didn’t realize that he only has around 50% of the climb performance that the aircraft would normally provide. Due to the high angle of attack he couldn’t see the terrain properly and therefore collides with tree tops on the ridge. The SUST assumes that the pilot was completely surprised by the collision.

LSPG, LSZC, Switzerland

I can’t easily translate the report, but 8% climb angle is going some, for a TB10.

Shoreham EGKA, United Kingdom

Peter wrote:

I can’t easily translate the report, but 8% climb angle is going some, for a TB10.

Neal has done the job for you in the essential things.

What has me puzzled are two things.
One: The aircraft was climbing way below it’s capability, only about 200-300 fpm, which is attributed to a procedure to climb with 2500 RPM. With normal climb performance as per POH, the aircraft should have been able to cross that ridge with 1000 ft to spare. Also, the minimum crossing height for the pass was 3500 ft AMSL, which was more than 500 ft higher than the airplane ever flew.

Two, why did the pilot turn northwards when over the Lake Alpnach, rather than go straight ahead towards Stansstaad when he realized he was low, The ridge he was trying to cross increases in elevation from south to north. All he would have needed to do is to stay slightly more south and he would have cleared the elevation.

It appears that due to the high pitch of the plane he never saw the ridge coming and must have been totally surprised when they hit the trees. 3-4 m higher,they would have cleared it.

That pilot was exceptionally experienced, a test pilot and chief pilot for a local airplane factory to whom the airplane belonged via its flight group. But he had very few recent experience on SEP and only 16 hours total time on the TB10, all of which had been a long time ago. The accident appears to show that experience in such cases can work against you.

LSZH, Switzerland

Mooney_Driver wrote:

With normal climb performance as per POH, the aircraft should have been able to cross that ridge with 1000 ft to spare

In theory, but we tend to get less than POH, not sure about TB10s but for a heavy M20J on similar day/altitude: WOT, Max Prop, full ROP at 85kts would get 500fpm while 26/26 give around 300-400fpm, so I would be impressed to see something around 900fpm

ESSEX, United Kingdom

Ibra wrote:

In theory, but we tend to get less than POH, not sure about TB10

Quite possibly so and DA was quite high that day.

However, with your M20J you operate with max power as you write. These guys apparently for some reason operated with 2500 rpm when max power is 2700 (fixed pitch prop). The POH of the TB10 sais clearly:

Climb: Full Rich, Full Power, 2700 RPM. According POH this results in 500-600 fpm climb under the conditions described in the report.

However, this club for some reason recommended to climb with 2500 RPM. According to the report they only ever climbed at about 200-300 fpm, which for me is very shallow at 2000-5000 ft. That is why the SUST concluded they were using 2500 RPM.

LSZH, Switzerland

Probably an engine management or fuel bill SOP which is of no use when climbing a mountain?

ESSEX, United Kingdom

Or noise abatement practice.

Keeping CHT lower by combining no leaning, less pitch and lower RPM.

LDZA LDVA, Croatia

Many clubs/groups/schools/airfields teach and practice a reduction to 2,500rpm shortly after takeoff in variable-pitch SEPs.

I was certainly taught/told this when I started flying the TB10, but it didn’t stick for me because I could see no rationale for it other than noise abatement. I fairly quickly moved to my current policy of all three levers fully forward and start nudging the mixture back to maintain constant EGT once I’m through about 2,000ft.

The problem with this common methodology of reducing to 2,500rpm is that, nice though it is for the neighbours, performance data in the POH is all based on max rpm.

I’ve never flow from anywhere high and I’m not sure how high I’d need to be before I considered leaning the TB10 for takeoff, but I don’t think it would be that high. As others have said, there is not exactly a surplus of power. Same power and similar MTOW to the Archer, but the TB10 trades performance for cabin space/comfort.

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